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In Situ Microstructure Modification Using a Layerwise Surface-Preheating Laser Scan of Ti-6Al-4V during Laser Powder
Ahmet Alptug Tanrikulu1,2, Behzad Farhang3,4, Aditya Ganesh-Ram3
1Materials Science and Engineering, The University of Texas at Arlington, Arlington, TX 76019, USA.
Materials (Basel, Switzerland)
|April 27, 2024
Summary
An innovative in situ thermal approach for titanium alloy (Ti-6Al-4V) fabrication via laser powder bed fusion (LPBF) enhances fatigue life by 10% without post-processing. This method optimizes microstructure and reduces surface roughness for superior mechanical properties.
Area of Science:
- Materials Science
- Additive Manufacturing
- Metallurgy
Background:
- Laser Powder Bed Fusion (LPBF) is a key additive manufacturing technique for titanium alloys.
- Achieving high fatigue life in LPBF-fabricated Ti-6Al-4V often requires post-processing steps.
- Microstructure and surface characteristics significantly influence the fatigue performance of metallic components.
Purpose of the Study:
- To investigate an in situ thermal approach to improve the fatigue life of Ti-6Al-4V fabricated by LPBF.
- To evaluate the effect of a preheating step on the material's microstructure and surface properties.
- To determine if post-processing can be eliminated by optimizing the in situ thermal treatment.
Main Methods:
- Implementation of an innovative in situ thermal process during LPBF of Ti-6Al-4V.
- Utilizing an additional laser scan with varied parameters for selective preheating of powder bed layers.
- Comparative analysis of preheated samples against reference samples fabricated without preheating.
- Microstructural characterization focusing on prior β-grain morphology, α lath thickness, and HCP α c/a ratio.
- Assessment of surface roughness and fatigue properties.
Main Results:
- The in situ preheating step significantly improved the fatigue life by 10% compared to reference samples.
- Optimized preheated samples exhibited a refined prior β-grain structure with circular morphology and thicker α laths.
- An increased c/a ratio in hexagonal close-packed (HCP) α phase was observed, indicating lattice strain relaxation.
- Reduced surface roughness was noted on the preheated samples.
- Enhanced overall mechanical strength was achieved alongside improved fatigue life.
Conclusions:
- The developed in situ thermal approach effectively enhances the fatigue life of LPBF-fabricated Ti-6Al-4V.
- Selective preheating during LPBF alters cooling rates, leading to favorable microstructural evolution and reduced surface roughness.
- This method offers a viable pathway to achieve superior fatigue performance without the need for post-processing treatments.
